Reliability of Alzheimer's Disease Assessment Scale - Cognitive (ADAS-Cog) tool varies widely

Nov 24 2008

A study published in the November issue of the Journal of Alzheimer's Disease (Volume 15:3) suggests the reliability of the Alzheimer's Disease Assessment Scale - Cognitive (ADAS-Cog) may vary and possess the ability to affect clinical trial outcomes.

Moreover, this study further suggests that ADAS-Cog rater training and experience are factors that contribute to variances seen in this assessment tool.

The importance of a reliable diagnosis of the Alzheimer's disease (AD) is critical as new pharmacotherapies are being developed. The ADAS-cog is considered the gold-standard and the most popular cognitive testing instrument used in clinical trials to detect changes in the core symptoms of AD.

This study critically looks at various factors that might influence the way the ADAS-cog is administered and therefore may lead to and yield unintended outcomes. The study found factors such as rater training, rater education, variance in time allotment during testing as well as rater experience and individual judgment may contribute to variance in scoring when using this assessment.

"Clinical trials for the possible treatment of Alzheimer's disease and other dementias are becoming more expansive and being run in many countries. The necessity for the primary outcome instrument to be administered consistently in different countries, cultures and between different clinical trials is critical if we are to determine which treatment works better than others. Any variability in how the instruments are administered can adversely affect the ability to detect positive outcomes," says Donald Connor PhD, PhD, director of neuropsychology at Banner Health's Sun Health Research Institute.

Rater experiences were not the only factors that contributed to variances in ADAS-cog scoring. The study also suggested that test materials changed over time including large ranges in the quality of naming materials, word card decks, instruction manuals and worksheets, all factors that can affect outcomes.

"Even as we try to develop better instruments for the detection of meaningful change we must make sure that our current instruments are utilized as effectively as possible," Dr. Connor says. "As the population continues to age rapidly and new Alzheimer's medications are being developed, it is critical that all who are involved in clinical evaluation and testing does so with precision and consistency."